The present invention relates to a liquid crystal display used for a liquid crystal projector and a sheet polarizer for the liquid crystal display.
A liquid crystal projector projects an image on a liquid crystal panel onto a screen on an enlarged scale using a projecting optical system. FIG. 3 shows one configuration of an optical system of a related art liquid crystal projector. The liquid crystal projector includes a lamp 101 for emitting light, a condenser lens 102 for condensing the light emitted from the lamp 101, an incoming light side sheet polarizer 103, an aperture 104, a liquid crystal panel 105, an outgoing light side sheet polarizer 106, and a projecting lens 107. The incoming light side sheet polarizer 103, which is referred sometimes to "a sheet polarizer before liquid crystal", allows only a specific polarized light component of the light condensed through the condenser lens 102 to pass therethrough. The aperture 104 has an aperture ratio of typically 50% for allowing 50% of the light component having passed through the incoming side sheet polarizer 103 to pass therethrough. The liquid crystal panel 105 has a number of pixels, and it allows the light component having passed through the aperture 104 to enter therein. The pixels are arranged, for example, in a grid pattern and are each capable of selecting a suitable optical rotatory power under a suitable electric field. The outgoing light side sheet polarizer 106, which is sometimes referred to as "a sheet polarizer after liquid crystal", is stuck on an outgoing light side face of the liquid crystal panel 105, and it allows only a specific polarized light component of the outgoing light component from the liquid crystal panel 105 to pass therethrough. The projecting lens 107 is adapted to project the light component having passed through the outgoing side sheet polarizer 106 on a screen 108 on an enlarged scale.
The liquid crystal panel 105 includes a drive substrate 111 on which a switching element using, for example, a thin film transistor (TFT) is formed for each pixel; a counter substrate 112 arranged opposite to the drive substrate 111 with a specific distance put therebetween; and liquid crystal 113 filled between the drive substrate 111 and the counter substrate 112. The liquid crystal panel 105 has, if needed, a color filter and the like for color display. In such a liquid crystal panel 105, the counter substrate 112 is disposed on the incoming light side; the drive substrate 111 is disposed on the outgoing light side; and the outgoing light side sheet polarizer 106 is stuck on the drive substrate 111.
In the liquid crystal projector shown in FIG. 3, light emitted from the lamp 101 is condensed through the condenser lens 102, and the condensed light enters in the incoming light side sheet polarizer 103. Only a specific polarized light component passes through the incoming light side sheet polarizer 103 as linearly polarized light. In the example shown in FIG. 3, at the incoming light side sheet polarizer 103, the quantity of transmitted light is taken as 3,000,000 lm, and the quantity of absorbed light is taken as 4,500,000 lm. The light having passed through the incoming light side sheer polarizer 103 enters in the liquid crystal panel 105. Assuming that the rate of aperture area is 50%, 50% of the incoming light component is cut off, and the remaining light component is selected in terms of optical rotatory power for each pixel and goes out of the liquid crystal panel 15 as elliptically polarized light suitable for each pixel. In the example shown in FIG. 3, at the liquid crystal panel 105, the quantity of transmitted light is taken as 1,500,000 lm, and the quantity of absorbed light is taken as 1,500,000 lm. The outgoing light from the liquid crystal panel 105 enters in the outgoing light side sheet polarizer 106. Here, the light component passes through the outgoing light side sheet polarizer 106 selectively for each pixel in accordance with the optical rotatory power for each pixel in the liquid crystal panel 105. In the example shown in FIG. 3, at the outgoing light side sheet polarizer 106, the quantity of transmitted light is taken as 0-1,350,000 lm, and the quantity of absorbed light is taken as 150,000-1,500,000 lm. The light having passed through the outgoing light side sheet polarizer 106 is projected on the screen 108 on an enlarged scale by the projecting lens 107, to form an image.
In the related art transmission type liquid crystal projector shown in FIG. 3, the two organic (iodine, dye) based sheet polarizers 103 and 106, each of which is substantially of the direct-vision type, are essentially provided as optical members before and after the liquid crystal panel 105, respectively. Also the existing liquid crystal projector is required to be increased in quantity of light, because the efficiency of the lamp 101 is low and the image is dark. In the related art liquid crystal projector, however, since the quantities of light absorbed by the sheet polarizers 103 and 106 become larger with the increased quantity of light, there is a fear that the sheet polarizers 103 and 106 are degraded by thermal energy or the like caused by light absorption at the sheet polarizers 103 and 106. As a result, the entire performance of the liquid crystal projector cannot be enhanced only by improving the durability of a single sheet polarizer with the related art configuration being left as it is.
In the related art liquid crystal projector, the sheet polarizers 103 and 106 and the liquid crystal panel 105 are air-cooled. However, for a liquid crystal projector used for AV (audio video), air-cooling cannot be sufficiently performed because of a limitation in terms of noise.
A thin polarizer directly contributing to polarization, which is low in humidity resistance, is generally used in the form of a sheet polarizer in which the polarizer is held between resin made protective layers for increasing the durability. However, the resin forming the protective layer generates heat, and thereby it shortens the service life of the sheet polarizer. Further, the resin having a low heat conductivity is liable to store the heat generated therein.
As the incoming light side sheet polarizer, an inorganic type polarizer such as a polarization beam splitter has been developed. However, the polarization beam splitter is very high in cost, and it is difficult to be adopted as a product for consumer use. For this reason, it is expected to develop a planar type polarization beam splitter; however, it is in the course of development and is poor in mass-production.
To increase the cooling efficiency of the liquid crystal panel 105, the outgoing light side sheet polarizer 106 should be separated from the liquid crystal panel 105; however, according to the existing technique, since unnecessary light caused by a difference in refractive index between the drive substrate 111 and air exerts adverse effect on operation of switching elements using TFTs or the like in the drive substrate 111 and in the worst case it makes impossible the driving, there is an limitation that the outgoing light side sheet polarizer 106 must be stuck on the drive substrate 111. Specifically, in the existing liquid crystal projector, the liquid crystal panel 105 must be used in such an undesirable state for cooling that the liquid crystal panel 105 and the outgoing light side sheet polarizer 106, each of which is a source of heat generation, must be integrated with each other.